Reflection is awesome it lets you handle class fields and methods dynamically, when using it, some of the common tasks that you will need are these:
- Get Class<T> instance. This class has the information of a given type.
- Create an instance of a given type.
- Get fields of type.
- Get a field by name
- Set value of a private field
- Set value of a private field using its setter method
- Get value of a private field
- Get value of a private field using getter method
- Get methods of the type
- Get method by name
- Call method by name
We are going to use this class for the examples
public class Foo {
private String bar;
public String getBar() {
return bar;
}
public void setBar(String bar) {
this.bar = bar;
}
public void printBar() {
printBar("");
}
public void printBar(String param) {
System.out.println(bar+param);
}
}
Get Class<T>
Class<Foo> clazz = Foo.class;Create an instance
try {
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
} catch (Exception ex) {
// handle exception
}Get fields of type
try {
Class<Foo> clazz = Foo.class;
Field[] fields = clazz.getDeclaredFields();
} catch (Exception ex) {
// handle exception
}Get a field by name
try {
String name = "bar";
Class<Foo> clazz = Foo.class;
Field field = clazz.getDeclaredField(name);
} catch (Exception ex) {
// handle exception
}Set value of a private field
try {
String name = "bar";
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
Field field = clazz.getDeclaredField(name);
field.setAccessible(true);
field.set(object, value);
} catch (Exception ex) {
// Handle exceptions
}Set value of a private field using its setter method
try {
String name = "bar";
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
String fieldName = name.substring(0, 1).toUpperCase() + name.substring(1);
String setMethod = "set" + fieldName;
Method method = clazz.getMethod(setMethod);
method.invoke(instance, value);
} catch (Exception ex) {
// Handle exceptions
}Get value of a private field
try {
String name = "bar";
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
Field field = clazz.getDeclaredField(name);
field.setAccessible(true);
Object value = field.get(instance);
} catch (Exception ex) {
// Handle exceptions
}Get value of a private field using getter method
try {
String name = "bar";
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
String fieldName = name.substring(0, 1).toUpperCase() + name.substring(1);
String getMethod = "get" + fieldName;
Method method = clazz.getMethod(getMethod);
Object value = method.invoke(instance);
} catch (Exception ex) {
// Handle exceptions
}Get methods of a type
Class<Foo> clazz = Foo.class;
Method[] methods = clazz.getMethods();Get method by name
try {
String name = "printBar";
Class<Foo> clazz = Foo.class;
Method method = clazz.getDeclaredMethod(name);
} catch (Exception ex) {
// Handle exceptions
}Call method by name
try {
String name = "printBar";
String param = "Foo";
Class<Foo> clazz = Foo.class;
Foo instance = clazz.getDeclaredConstructor().newInstance();
Method method = clazz.getMethod(name, String.class);
Object value = method.invoke(instance, param);
} catch (Exception ex) {
// Handle exceptions
}